Rail Builder

print("Length?")
local length = tonumber(read())

local segments = length/8

local brickItem = "MineFactoryReloaded:brick"
local concreteItem = "Railcraft:cube"
local railItem = "minecraft:rail"
local lanternItem = "Railcraft:lantern.stone"

function selectItem(name)
  local thisSlot = turtle.getItemDetail()
  if (thisSlot ~= nil) then
    if (thisSlot.name == name) then
      return
     end
  end
  for i=1,16 do
    local data = turtle.getItemDetail(i)
    if (data ~= nil) then
      if (data.name == name) then
        turtle.select(i)
        return
      end
    end
  end
  return false
end

function getItemCount(name)
  local sum = 0
  for i=1,16 do
    local data = turtle.getItemDetail(i)
    if (data ~= nil) then
      if (data.name == name) then
        sum = sum + data.count
      end
    end
  end
  return sum
end

function clearInventory()
    for i=1,16 do
        local slot = turtle.getItemDetail(i)
        if (slot ~= nil) then
            if (not(slot.name == brickItem or slot.name == concreteItem or slot.name == railItem or slot.name == lanternItem)) then
                turtle.select(i)
                if (slot.name == "minecraft:log") then
                    turtle.refuel()
                else
                    turtle.dropDown()
                end
            end
        end
    end
end

function checkItem(name,count)
  local c = getItemCount(name)
  while (c < count) do
    print("Add more ["..name.."] and press enter.")
    read()
    c = getItemCount(name)
  end
end

function checkFuel()
    local fuelLevel = turtle.getFuelLevel()
    local fuelEstimate = (length * 5) + (segments * 32)
    print("Fuel Level: "..fuelLevel.." Estimated needed: "..fuelEstimate)
    if (fuelLevel < fuelEstimate) then
        print("Not enough fuel. Refuel and try again.")
        os.sleep(2)
        shell.exit()
    end
end

function buildColumn()
  local depth = 0
  while(true) do
    local success, block = turtle.inspectDown()
    if (success and (block.name == "minecraft:grass" or
        block.name == "minecraft:dirt" or
        block.name == "minecraft:stone" or
        block.name == "minecraft:sand" or
        block.name == "minecraft:sandstone" or
        block.name == "minecraft:gravel" or
        block.name == "minecraft:bedrock")) then
        break
    else
        if (success) then
            turtle.digDown()
        end
        turtle.down()
        depth = depth + 1
    end
  end
  for i=1,depth do
    if (i == depth-1) then
         turtle.turnRight()
         selectItem(concreteItem)
         turtle.place()
         turtle.turnLeft()
         turtle.turnLeft()
         selectItem(concreteItem)
         turtle.place()
         turtle.turnRight()
       end
    turtle.up()
    selectItem(concreteItem)
    turtle.placeDown()
  end
  turtle.up()
  selectItem(lanternItem)
  turtle.placeDown()
  turtle.forward()
  turtle.down()
end

function buildRails()
    for i=1,8 do
        turtle.down()
        --Place bricks
        turtle.turnRight()
        if (turtle.detect()) then
            turtle.dig()
        end
        selectItem(brickItem)
        turtle.place()
        turtle.up()
        if (turtle.detect()) then
            turtle.dig()
        end
        selectItem(railItem)
        turtle.place()
        turtle.turnLeft()
        turtle.turnLeft()
        turtle.down()
        if (turtle.detect()) then
            turtle.dig()
        end
        selectItem(brickItem)
        turtle.place()
        turtle.up()
        if (turtle.detect()) then
            turtle.dig()
        end
        selectItem(railItem)
        turtle.place()
        turtle.turnRight()
        if (i ~= 8) then
            turtle.forward()
        end
    end
end

checkFuel()

--Official Loop
for i=1,segments do
  checkItem(brickItem, 16)
  checkItem(railItem, 16)
  checkItem(concreteItem, 64)
  checkItem(lanternItem, 1)
  print("Constructing segment "..i)
  buildRails()
  buildColumn()
  clearInventory()
end